I think the actual reason of why he's assignee there is because he's too powerful, and that wouldn't be good for the demon king or some other higher ups.
when he walk toward their robbed party member, his floating hands were restrained by the robbed figure's chains and the girl throw some special sword to his back while gloating. Then he just fall and losing consciousness which led to flashbacks on how he started.....
I wonder if the mid boss got sent here not because the demon king trusted him but he was afraid of him taking over and so sent him in the middle of nowhere
@kaikalaila : If you can link me a raw location without ads/paywall I can try to give you a summary :v the raw link on the main page doesn't have ch 6 viewable.
wot? so u guys telling me he got fucked up in the next chap? maybe then saved by the other dungeon monsters?the heck i tought he was going to destroy the hero party after turbo fucking the 'wise man'